Identifying Invasive Plants
When settlers began gardening, they had a constant struggle to keep the natural ecosystem from invading and overwhelming their small cultivated patches. Today, humans have so altered the Midwest landscape that the reverse is true: Many of the plants we’ve cultivated have escaped and are now threatening to out-compete more favorable native plants in conservation areas.
What’s Wrong with That?
Invasive plants out-compete other species for water, nutrients, sunlight, and space. As a result, invasive species can:
- Displace native species
- Reduce plant diversity
- Alter ecosystem processes
- Hybridize with native plants, changing their genetic makeup
- Destroy the habitats that support native animals, insects, and micro-organisms
- Create ecosystems that support aggressive, non-native plants, animals, and pathogens
Categories of Invasive Plants
- Exotics—These are primarily European or Asian species that have been accidentally introduced or intentionally imported for their ornamental value or their ability to provide shade, windbreaks, and erosion control.
- Translocators—These are native species that have moved out of their original range into an area that favors their over-production.
- Opportunists—These are native colonizing species that, previously, may have been held in check by natural processes.
What Makes Plants Invasive?
Researchers believe there are several factors that contribute to a plant becoming invasive. These include:
- Fast growth rate
- Seeds that germinate quickly in high percentage
- Prolific seed production, which begins within the first few years of the plant’s life
- Easy seed dispersal by animals, water, and wind
- Ability to reproduce by seed as well as vegetatively, through suckering for instance
- Longer flowering and fruiting periods
- Adaptability to a wide range of soil and growing conditions
Identifying and Managing Invasive Trees, Shrubs, and Vines
On the inside chart, The Morton Arboretum offers a list of native and non-native trees, shrubs, and vines that are already persistent problems or have the capacity to become problematic in the home landscape and adjacent natural areas. Some of these plants are so invasive that their sale has become illegal in some states. Researchers at the Arboretum, as well as state and federal authorities, continue to examine and identify plants that have the potential to become invasive.
Are All Exotic Plants Bad?
The majority of exotic plants are not problematic and pose no threat to our natural areas. Exotic plants play an important role in modern day landscapes offering tough, resilient, and aesthetically pleasing additions to yards, streets, and urban campuses.
Controlling Invasive Plants
Invasive plants can generally be controlled by mechanical, cultural, and/or chemical methods. Here are some resources to learn more about control methods:
- Invasive Plants:Weeds of the Global Garden published by Brooklyn Botanic Garden, www.bbb.org
- University of Illinois Extension Office. To find your local office, call 217-333-5900 or go to www.extension.uiuc.edu. or www.aces.uiuc.org
- Wisconsin Manual of Control Recommendations for Ecologically Invasive Plants published by the Bureau of Endangered Resources, Wisconsin Department of Natural Resources 608-266-7012.
|Common/Botanical Name||Description||Origin||Reproductive Capacity||Invasive Potential|
|Amur Maple Acer ginnala||A small (20’) tree with double-tooth-edged leaves have shallow lobes. In spring, small fragrant, pale yellow flowers appear as leaves unfold. Two-winged, inch-long seeds mature in late summer.
||Native of Eastern Asia. Introduced into U.S. and Canada in 1860s.||One tree can produce more than 5,000 two-winged seeds that are widely spread by wind.||In open woods, it displaces native shrubs and understory trees. In prairies and open fields, it can shade out native species.|
|Boxelder Acer negundo||Large (30-50’) tree adaptable to wet or dry soils. Leaves have 3-5 leaflets opposite each other on the stem. Female trees produce many two-winged seeds. New stems are a waxy gray-blue, turning green when rubbed.||Native to U.S., particularly along riverbanks and floodplains.||It can spread by suckers, root shoots, and a prolific number of wind-borne seeds. It readily establishes in disturbed areas, including fencelines, near buildings, abandoned roads, railroad beds, dumps, and farm fields.
||It quickly establishes thickets that shade out smaller, more desirable plants.|
|Norway Maple Acer platanoides||A 40-50’ tree with a leaf shape like its cousin the sugar maple. Unlike the sugar maple, Norway maple leaves have a milky sap when broken, and their fall color is limited to yellow (except for the maroon-leaved varieties).
||Native to Europe, this tree was introduced in Philadelphia in 1792 as an ornamental street tree. Today, it is the most commonly planted street tree in the U.S.||It spreads by prolific production of wind-borne, two-winged seeds.||It is easily established in open woodlands and fields. Shade tolerant and an efficient user of water and nutrients, it can out-compete native sugar maple and beech. Its dense canopy limits wildflowers and other understory herbaceous growth.
|Porcelain Vine Ampelopsis brevipedunculata||Perennial vine with deeply lobed leaves, which are sometimes variegated. In fall, its abundant clusters of large, shiny berries turn blue and||Introduced from northeast Asia in 1870.||Its abundant seeds have a very high germination rate. It also reproduces vigorously from its roots and from stems in contact||This vigorous vine forms a tangle that covers the ground as well as woodland trees and shrubs, blocking out sunlight and competing for nutrients and water. It|
|purple mottled with white and gray.||with the soil.||colonizes at woodland edges and gaps, as well as in any sunny, disturbed area, such as highway shoulders, railroad beds, riverbanks, shorelines, and fields.|
|Japanese Barberry Berberis thunbergii||This shrub grows 36’ tall. It is most easily identified by its small, rounded leaves, spiny stems, and red berries that||Native to Asia, it was introduced around 1875.||Birds and rodents eat the fruits and distribute the seeds widely. Its branches form roots when in||It invades woodlands, preventing growth of understory shrubs and other plants.|
|develop in summer.||contact with the soil. This, and the|
|shrub’s vigorous root system, helps it form thickets.|
|Oriental Bittersweet||A deciduous,||Native to Asia, this||Birds are the||This vine flourishes in|
|Celastrus orbiculatus||twining vine that can grow to five inches in diameter and up to 60 feet long. It is differentiated from American bittersweet by its yellow and red fruits, which appear all along the stems. American||plant was introduced in the mid 1800s. Grown for its berries which are used in flower arrangements.||primary means of seed dispersal. This plant also spreads vigorously through suckers.||open woods, thickets, and roadsides where it aggressively competes for water, nutrients, and sunlight. Through twining, it restricts the host plant’s sap flow. It can also make the host top-heavy and subject to wind damage.|
|fruit only at the stem tips.|
|Autumn-olive Elaeagnus umbellata||This shrub can grow up to 20’ high and wide. Its gray-green leaves are shorter and less silvery than Russian-olive. It has fragrant yellow flowers that emerge after the leaves in||Native to Asia, this plant was introduced in 1917. Valued for its use as a forage plant in wildlife areas, this vigorous shrub now dominates many untended areas from fencerows to meadows||Just one shrub can produce up to 200,000 seeds a season. These are widely distributed by birds.||This shrub grows rapidly into a dense thicket, choking out native plants.|
|spring and mature into bunches of red||to open woods, sand dunes, and railroad|
|fruits in fall.||rights of way.|
|Burning Bush Euonymus alatus||Burning bush is often 12’ tall and can reach 15-20’ high and wide. It’s identified easily by four corky “wings” on the stems and its brilliant red fall color.||Native to northeast Asia, this plant was introduced in the 1860s for its ornamental value.||This shrub is spread by birds that eat the seeds. It can tolerate many conditions, from full sun to nearly full shade and from very dry to moist soils.||This shrub has begun invading open woodlands, mature second-growth forest ravines, and hill prairies, out-competing many native plants. Rarely a problem in urban landscapes.|
|European Privet Ligustrum vulgare||This deciduous shrub grows 12-15’ high and wide. This densely-branched, irregularly shaped plant is most easily identified by its clusters of fragrant small white flowers||Native to Europe, this plant was introduced into the U.S. around 1850 and has been widely used for hedges.||Birds spread the seeds of this prolific producer. The plant also suckers aggressively.||This extremely aggressive shrub is crowding out native plants along natural areas including river bottoms, and open woods, as well as in fencerows, vacant lots, old fields, and roadsides.|
|from May through June. Its lustrous|
|black fruit ripens in fall and remains on|
|the shrub often until|
|the following spring.|
|Japanese Honeysuckle Lonicera japonica||Semievergreen woody vine that has fragrant, tubular flowers that start white (may be tinged with pink or purple), and turn yellow as they mature. The twining vine grows 15-30’ long and has black berries that||A native of eastern Asia, this plant was introduced into New York in 1806.||The vine is spread by birds that eat the fruits. It grows aggressively and has become such a problem that its sale and distribution are prohibited in Illinois.||This vine spreads rapidly, crawling along fields, fencerows, and roadsides smothering everything in its path. In woodlands, it grows over the tops of trees and shrubs, engulfing them.|
|ripen in fall.|
|Amur Honeysuckle Lonicera maackii||This upright, spreading, leggy deciduous shrub grows 12-15’ tall and wide. It can best be differentiated from native species because it leafs out several weeks earlier in spring and holds its leaves longer in fall. It has white, 1”-||Native to Asia, this plant was introduced into North America in 1896. Illinois is one of the states where it has been most invasive.||In addition to being a vigorous, aggressive grower, Amur honeysuckle seeds are widely spread by birds.||Amur honeysuckle colonizes a wide variety of habitats, turning prairies into scrub and reducing the plant diversity and density of woody seedlings in the ground layers of woodlands. Because they leaf out early, they shade out spring-blooming woodland wildflowers.|
|long flowers that turn yellow, and red berries that ripen in October.|
|White Mulberry Morus alba||Deciduous tree growing 30-50’ tall and wide. Its extremely dense, rounded form is composed of tight-knit slender branches, often developing witches’ broom. Its leaves||Native to China, this plant was imported by early settlers in Jamestown, Virginia for the silkworm industry.||This tree is spread by birds who love its berries. The white mulberry flourishes in a variety of cultural conditions and adapts to drought, salt, and urban soils.||This tree is rarely a problem in undisturbed woodlands. It naturalizes in disturbed woodlands, and along railroads, back alleys, floodplains, and open lots.|
|may be either undivided or lobed.|
|In summer, it|
|develops fruits resembling blackberries.|
|Amur Corktree Phellodendron amurense||This medium-sized shade tree grows 3045’ tall with an equal or greater spread. Its compound leaves are 10-15” long and include 5-11 leaflets.||Native to Asia, this tree was introduced to the U.S. in 1856.||Seeds spread by birds. Establishes itself in woodlands and along streams.||Female plants produce seed and should be avoided. Seedless male selections are becoming available in the nursery trade.|
|The bark of older|
|trees is gray-brown and cork-like in|
|Inconspicuous yellow-green flowers appear in late spring followed by ½” black fruits which|
|have an unpleasant odor when bruised.|
|Common Buckthorn Rhamnus cathartica||A tall shrub/small tree that can grow to||Native to Europe and Asia, these plants were||Birds widely disperse its seeds.||Bird-dispersed seed has a high germination rate in a|
|20’ tall. The leaves,||introduced during the||Once established,||variety of habitats|
|which appear earlier||1800s as ornamental||this plant quickly||including gardens,|
|than most natives in||hedgerows.||develops dense||fencerows, pastures,|
|spring and persist||thickets that out-||prairies, roadsides, and|
|beyond most natives||compete other||abandoned farm fields. In|
|in fall, are a dull||plants. It grows||woodlands, it can|
|green and elliptical.||rapidly in a variety||completely replace|
|Twigs often have||of conditions, from||existing understory plants,|
|thorn-like spurs.||full sun to shaded||including spring-|
|Female plants bear||understory, and||flowering wildflowers.|
|round, dark blue||resprouts|
|fruits in May and||vigorously when|
|June that ripens to||cut back.|
|black in August and|
|may persist for much|
|of the winter.|
|Glossy Buckthorn Rhamnus frangula||This multi-stemmed shrub/small tree can grow 10-15’ tall. The elliptical leaves, which appear earlier than most natives in spring and persist beyond most natives in fall, are glossy green on top and somewhat hairy underneath. Female plants bear round, red fruits in May and June that ripen to black in August and may persist for much of the winter.||Native to Europe and Asia, these plants were introduced during the 1800s as ornamental hedgerows.||Birds disperse its seeds. Once established, this plant quickly develops dense thickets that out-compete other species. Although it favors wetlands, it can also become established on dry sites. It grows rapidly in a variety of conditions, from full sun to shaded understory, and resprouts vigorously when cut back.||Bird-dispersed seed has a high germination rate in a variety of habitats including bogs, marshes, river banks, pond margins, gardens, fencerows, pastures, prairies, roadsides, abandoned farm fields. It is much less shade tolerant than common buckthorn.|
|Black Locust Robinia pseudoacacia||This fast-growing tree reaches 30-80’ tall. Its dark blue-||This tree is native to the eastern U.S. Its rapid growth,||Black locust creates expansive, dense stands||Outside its original range this tree can out-compete native species in most dry,|
|green leaves are 6||extensive, soil-holding||through seed||disturbed environments|
|14” long with 7 to||root system, high fuel||germination and||including upland forests,|
|21 leaflets. In May||value, and flowers that||suckering.||savannas, prairies,|
|to early June, the||provide an attractive||pastures, roadsides, and|
|tree has fragrant,||food source for bees||old fields. Its seeds,|
|white, pea-like||are among the reasons||leaves and bark are toxic|
|flowers in large,||it was widely planted.||to humans and animals.|
|Later, shiny, flat, 2|
|4” long seedpods|
|Multiflora Rose Rosa multiflora||A dense, spreading shrub that can grow 10-15’ tall with arching canes and stiff, curved thorns.||A native of Japan, this plant was introduced in 1886 as rootstock for cultivated roses. Later, the U.S. Soil||A single plant can produce up to 500,000 seeds a year. These seeds can remain viable||Multiflora rose readily invades pastures, prairies, savannas, open woodlands, forest edges, and roadsides.|
|Unlike native roses, which usually have pink blossoms, the multiflora has clusters of white||Conservation Service encouraged its planting to curb soil erosion.||in the soil for up to 20 years. In addition to dispersal by birds, multiflora rose can|
|flowers, which||create dense|
|mature into ¼” red seeds or “hips” that persist through the winter.||thickets by suckering.|
|Poison Ivy Toxicodendron radicans||This plant grows as a vine that climbs trees, a ground cover, or an upright shrub. Although its leaves are somewhat variable, they normally appear as three leaflets. This plant produces small, off-white||This native species is opportunistic and can become very aggressive in any areas disturbed by human activities including trails, parks, yards, recreation areas, dunes, shorelines, and woodlands.||Spreads by seed and vigorous growth. Often found in abandoned fencerows and clinging to large mature trees.||Although there is little evidence that poison ivy is threatening native flora, it is very troublesome to most people. Oils from the leaves and stems, as well as smoke from burning poison ivy, can cause potentially serious dermatitis.|
|flowers and later|
|yellow-white berries that are usually hidden by the foliage. In fall, leaves turn a brilliant|
|Siberian Elm Ulmus pumila||This fast-growing tree is 50-70’ tall with a round, open crown. It has small, elliptical leaves that are usually less than 2 inches long. Greenish flowers appear in small, drooping clusters before the leaves||A native of Asia, this tree was introduced to the U.S. in the 1860s. It was valued for its rapid growth and ability to adapt to a variety of conditions, including poor soil and drought.||Windswept seeds germinate prolifically, often forming thickets of hundreds of seedlings.||This tree can dominate a prairie in a few years. It also invades roadsides, pastures, streambeds, and sand prairies.|
|unfurl in spring. Later, the one-|
|seeded, winged fruits hang in clusters.|
|European Cranberry-bush Viburnum opulus||Upright, spreading shrub that grows up to 15’ tall and wide. Its maple-shaped leaves are glossy dark green. They may remain green until they drop in fall or change to yellow-red or purple-red. Bright red, berrylike fruits ripen in fall and persist into winter.||Native to Europe, this plant was introduced in the second half of the 17th century for its ornamental qualities as well as its adaptability to many conditions.||Seeds are widely distributed by birds.||This prolific plant is starting to naturalize in wetlands and forests as well as degraded woodlands near urban and suburban areas, where it is displacing native species.|
*Invasive categories obtained from the following sources: